AFRICA
The climates of Africa are both spatially varied and varying temporally: spatially varied because they range from humid equatorial regimes, through seasonally-arid tropical regimes, to sub-tropical Mediterranean-type climates, and varying because all these climates exhibit differing degrees of temporal variability, particularly with regard to rainfall. Understanding and predicting these inter-annual, inter-decadal and multi-decadal variations in climate has become the major challenge facing African and
African-UNIVERSITAT ROVIRA I VIRGILI
CLIMATE CHANGE ANALYSIS FOR GUINEA CONAKRY WITH HOMOGENIZED DAILY DATASET.
Abdoul Aziz Barry Dipòsit Legal: T 262-2015
Climate change analysis for Guinea Conakry with homogenized daily dataset 38 specialist climate scientists in recent years (Hulme et al., 2001; AR5). In the following paragraphs we will have a look at climate change in Africa, we will start by giving an overview of Guinea climate characteristics and climate change; This will be followed by the outcome of up to date studies of African climate change and variability over the last century, based on the observational record of Africa climate, and finally we will present the projected climate change for Africa from GCM and RCM results deposited with the IPCC.
Most of Africa is insufficiently sampled by climatic observations to allow an overall and high certainty evaluation about the continental scale changes. However, there is some evidence of changes in temperature extremes from the observations gathered since 1950, since most of the regions on this continent for which data are available have exhibited warming in temperature extremes. In earlier available analyses on climate change in Africa including Kruger et al. (2006); New et al. (2006); and most recently, Aguilar et al.
(2009), the results are consistent with the assessment of an increase in warm days and nights and a reduction in cold days and nights on the regional basis, although the referred studies do not necessarily consider trends in all four variables. Only a few studies report trends that are not statistically significant or even trends opposite to the global tendencies occur in some extremes, sub-regions, seasons, or decades. As a general result in Kruger and Sekele (2013) state that warm extremes have increased and cold extremes have decreased over South Africa; the trends however vary on a regional basis. In a previous study by New et al. (2006) the same result for the eastern part of southern and WA was reported. Recent available studies also suggest that the number of cold spells has decreased significantly since the 1950s (Donat et al., 2013a, 2013c). Confidence in observed trends in daily temperature extremes in Africa and generally varies from low to medium depending on the region (Kuglitsch et al., 2009; IPCC, 2012).
According to IPCCI (2012a) there is low to medium confidence in regional trends in heavy precipitation in Africa due to the partial lack of data and data analysis, and due to the lack of consistency in reported trends. Seneviratne et al. (2012) and Trenberth et al.
(2007) reported an increase in heavy precipitation over southern Africa, but this appears to depend on the region and precipitation index examined (Kruger, 2006; New et al., 2006; Seleshi and Camberlin, 2006; Aguilar et al., 2009). Central Africa exhibited a decrease in heavy precipitation over the last half century (Aguilar et al., 2009), however,
UNIVERSITAT ROVIRA I VIRGILI
CLIMATE CHANGE ANALYSIS FOR GUINEA CONAKRY WITH HOMOGENIZED DAILY DATASET.
Abdoul Aziz Barry Dipòsit Legal: T 262-2015
39 Climate change analysis for Guinea Conakry with homogenized daily dataset data coverage for large parts of the region was poor. Precipitation from heavy events has decreased in western central Africa, but with low spatial coherence (Aguilar et al., 2009).
Rainfall intensity averaged over southern and WA has increased (New et al., 2006).
Camberlin et al. (2009) analyzed changes in components of rainy seasons’ variability over the time period 1958-1987 in Equatorial East Africa, but did not specifically address trends in heavy precipitation. There were decreasing trends in heavy precipitation over parts of Ethiopia during the period 1965-2002 (Seleshi and Camberlin, 2006). There is medium confidence that since the 1950s some regions have experienced a trend to more intense and longer droughts, in particular in WA, but in some other regions droughts have become less frequent, less intense, or shorter (Seneviratne et al., 2012).
There are still large uncertainties regarding observed drought trends in Africa stated AR5.
Data availability, quality and length of record remain issues in drawing conclusions on the continental scale. Additionally, the type of drought considered and the complexities in defining drought can substantially affect the conclusions regarding trends on a large scale.
Nonetheless, there is some agreement between studies over different time frames and using different drought indicators regarding the increasing drought occurrence in WA according to AR5. New analyses continue to support the AR4 and SREX conclusions.
Hartmann et al. (2013) also indicated that it is likely that the frequency and intensity of drought has increased in the Mediterranean and WA. Recent available studies also suggest that the number of cold spells has reduced significantly since the 1950s (Donat et al., 2013a, 2013c).
According to Perkins et al. (2013), owing to lack of studies over Africa but also in part owing to differences in trends depending on how heat waves are defined, confidence in heat waves changes is medium.
Based on updated studies, AR4 conclusions regarding global increasing trends in drought since the 1970s were probably overstated (Hartmann et al., 2013). However, this masks important regional changes: the frequency and intensity of drought have likely increased in the Mediterranean and WA.
Overall, Africa assessments are consistent with the global assessments provided previously. It should be noted, however, that the assessed uncertainty is larger at the
UNIVERSITAT ROVIRA I VIRGILI
CLIMATE CHANGE ANALYSIS FOR GUINEA CONAKRY WITH HOMOGENIZED DAILY DATASET.
Abdoul Aziz Barry Dipòsit Legal: T 262-2015
Climate change analysis for Guinea Conakry with homogenized daily dataset 40 regional level than at the continental or global level. Global-scale trends in a specific extreme may be either more reliable or less reliable than regional-scale trends, depending on the geographical uniformity of the trends in the specific extreme. Hence, Seneviratne et al. (2012) assess that in terms of absolute values, the 20-year extreme annual daily maximum temperature will likely increase by about 2 to 5°C by the late 21st century, and by about 1 to 3°C by mid-21st century, depending on the region and emissions scenario.
A widespread decrease in the maximal annual temperature range over WA, the Sahel, and the Congo basin is expected. Both twenty first century Tx and Tn are projected to increase, but the magnitude of the increase is greater for the Tn. Mid twenty first century Tx and Tn are projected to increase in all regions with regional and seasonal variations that affect the daily temperature range. The DTR over WA and Central Africa during the boreal spring and fall, over the Sahel during May–September, and over the Congo basin during the boreal winter and spring is projected to decrease. Conversely, the DTR (Daily Temperature Range) will increase over the Horn of Africa during the boreal winter and over Kenya– Tanzania during the boreal summer associated with greater warming of Tx due to a decrease in atmospheric relative humidity (Vizy et al., 2012; Kirtman et al., 2013).
Simulations by 12 GCMs (General Circulation Models) projected an increase in heavy precipitation intensity and mean precipitation rates in east Africa, more severe precipitation deficits in the southwest of southern Africa, and enhanced precipitation further north in Zambia, Malawi, and northern Mozambique (Shongwe et al., 2009, 2011).
The number of dry days is predicted to decrease over the Congo basin and over central Africa and the Sahel east of 08East in the mid-twenty-first century. Inversely, over East Africa, the number of dry days is projected to increase.
Extreme wet days are predicted to increase over WA, the southern Sahel, the Ethiopian Highlands, and over Somalia. Over Congo basin decrease is projected in the number of extreme wet days. Extreme wet day rainfall intensity is projected to decrease over most western Africa countries and increase over the horn of Africa.
UNIVERSITAT ROVIRA I VIRGILI
CLIMATE CHANGE ANALYSIS FOR GUINEA CONAKRY WITH HOMOGENIZED DAILY DATASET.
Abdoul Aziz Barry Dipòsit Legal: T 262-2015
2.5. Observed and projected climate change in Africa
41 Climate change analysis for Guinea Conakry with homogenized daily dataset Over WA both the number of dry and intense rainfall days during the boreal summer are projected to increase indicating that the summer rainfall will be delivered in fewer, but more intense events.
Over the Sahel the number of extreme dry days is projected to decrease, while the number of extreme heavy rainfall days increases. Rainfall is projected to intensify over the Congo during the boreal spring and weaken in the fall and winter, with opposite results to the east over Kenya and Tanzania. These changes in extreme precipitation will have important implications for the agricultural sector as most of Africa relies on rain-fed agricultural practices. An improved understanding of how rainfall will be delivered over the annual cycle will support the development of adaptation strategies (Vizy et al., 2012;
Kirtman et al., 2013).
Available global and regional studies of hydrological drought (Hirabayashi et al., 2008;
Feyen and Dankers, 2009) project a higher likelihood of hydrological drought by the end of this century, with a substantial increase in the number of drought days (defined as stream flow below a specific threshold) during the last 30 years of the 21st century over central and southern Africa.
Significant increase in the number of heat wave days is predicted over most of the Sahel and Saharan Africa. There is also a projected increase in heat wave days in northernmost WA and central Africa primarily during boreal springtime.
Death and hospitalizations linked to heat waves are likely to increase over the Sahara and Sahel, but also to extend equator ward over tropical Africa into areas that up to now do not experience such events.
By the mid twenty first century there will likely be a shift to warmer extreme temperatures over sub-Saharan and tropical Africa, although the severity of these changes is not uniform across the annual cycle and is regionally dependent (Vizy et al., 2012;
Kirtman et al., 2013).
UNIVERSITAT ROVIRA I VIRGILI
CLIMATE CHANGE ANALYSIS FOR GUINEA CONAKRY WITH HOMOGENIZED DAILY DATASET.
Abdoul Aziz Barry Dipòsit Legal: T 262-2015